麴

Two distinct uses. As a common noun, 麴 is a high-register / traditional variant of 曲 (the 'yeast / starter' sense). The modern simplified standard collapsed both into 曲, so in mainland publications you will typically see 酒曲 (jiuqu, liquor starter) rather than 酒麴. The 麴 form survives in Taiwan, Hong Kong, traditional-character writing, and historical / culinary scholarship. As a surname, 麴 is the Qu family — most famous as the rulers of the Tang-era Gaochang Kingdom on the Silk Road.

Even in traditional-character contexts, the surname is sometimes written 曲 rather than 麴. Mainland identity documents standardise to 曲; people whose family records preserve the 麴 spelling may keep it for cultural / genealogical reasons.